Historical Geology Understanding Our Planet\'s Past

flows, tillites, and coal beds, reaching a total thickness of 20,000 feet. Between

layers of coal were fossil leaves of the extinct fern Glossopteris.Because this

plant is found only on the southern continents, it is among the best evidence

for the existence of Gondwana.

After an examination of the earliest land plants of the Silurian,the next

chapter will focus on the marine life of the Devonian period.

Figure 90Extent of late
Paleozoic glaciation in
Gondwana.

Historical Geology

AFRICA

SOUTH AMERICA

ANTARCTICA

AUSTRALIA

INDIA